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I was surprised today when I discovered that GeoMarker seems to ignore the Opacity directive in GeoGraphics. This can be demonstrated using the first example in the documentation:

GeoGraphics[{GeoStyling["OutlineMap"], 
  Opacity[.5],
  Polygon[Entity["Country", "Italy"]], 
  GeoMarker[Entity["City", {"Rome", "Lazio", "Italy"}]]}]

wrong opacity

The country's polygon is respecting the Opacity directive, but GeoMarker ignores it.

How to properly set the opacity of GeoMarkers?

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Probably the most simple way to set the opacity of GeoMarkers is with an undocumented usage of its "Color" parameter. It appears to support Directives, so the opacity can be set the following way:

GeoGraphics[{GeoStyling["OutlineMap"], Opacity[.5], 
  Polygon[Entity["Country", "Italy"]], 
  GeoMarker[Entity["City", {"Rome", "Lazio", "Italy"}], 
   "Color" -> Directive[Opacity[.5], RGBColor[0.790588, 0.201176, 0.]]]}]

correct opacity

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  • $\begingroup$ Do you mind tell us how to find it? $\endgroup$ – yode Jun 18 '16 at 16:22
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    $\begingroup$ @yode I had a hunch and was lucky it worked. :) $\endgroup$ – shrx Jun 18 '16 at 16:30
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    $\begingroup$ "Color" is a documented option for GeoMarker $\endgroup$ – Bob Hanlon Jun 18 '16 at 18:24
  • $\begingroup$ @BobHanlon Yes, but it doesn't mention it can take other arguments than color objects. $\endgroup$ – shrx Jun 18 '16 at 18:38
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    $\begingroup$ [RGBColor] (reference.wolfram.com/language/ref/RGBColor.html) has an optional fourth argument for opacity. $\endgroup$ – Bob Hanlon Jun 18 '16 at 20:03

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